Abstract
Social animals have to coordinate joint movements to maintain group cohesion, but the latter is often compromised by diverging individual interests. A widespread behavioral mechanism to achieve coordination relies on shared or unshared consensus decision-making. If consensus costs are high, group fission represents an alternative tactic. Exploring determinants and outcomes of spontaneous group decisions and coordination of free-ranging animals is methodologically challenging. We therefore conducted a foraging experiment with a group of wild redfronted lemurs (Eulemur rufifrons) to study decision outcomes, coordination of movements, individual foraging benefits and social interactions in response to the presentation of drinking platforms with varying baiting patterns. Behavioral observations were complemented with data from recordings of motion detector cameras installed at the platforms. The animal's behavior in the experimental conditions was compared to natural group movements. We could not determine the type of consensus decision-making because the group visited platforms randomly. The group fissioned during 23.3% of platform visits, and fissioning resulted in more individuals drinking simultaneously. As under natural conditions, adult females initiated most group movements, but overtaking by individuals of different age and sex classes occurred in 67% of movements to platforms, compared to only 18% during other movements. As a result, individual resource intake at the platforms did not depend on departure position, age or sex, but on arrival order. Aggression at the platforms did not affect resource intake, presumably due to low supplanting rates. Our findings highlight the diversity of coordination processes and related consequences for individual foraging benefits in a primate group living under natural conditions.
Highlights
Group-living holds a number of benefits, and costs for individual group members
Only one individual decides, e.g. when to change place and activity, irrespective of other individuals’ interests, and all group members abide by this decision
We explored the circumstances favoring group fissioning, predicting group fission rates – as a means to avoid costly consensus decisions in the first place by foraging in independent subgroups – (i) to decrease when the number of baited platforms was reduced, and (ii) to increase after the group visited a poorly baited platform where only one group member has access to a valuable resource instead of five
Summary
Group-living holds a number of benefits, and costs for individual group members. Group-living animals can reach a consensus via a continuum of decision-making processes, depending on the proportion of group members involved in the decision. Only one individual decides, e.g. when to change place and activity, irrespective of other individuals’ interests, and all group members abide by this decision. Between these two extremes, consensus decisions can be more or less partially shared [4,8]
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